1. Field of the Invention
The invention relates to fuel injector assemblies for internal combustion engines, and more particularly to the arrangement of conduits within fuel injector assemblies.
2. Description of the Related Art
A fuel injector assembly of well-known design, including a fuel injection pump and a control valve self-contained in a unit, is illustrated in FIG. 1. The fuel injector assembly 10 comprises a pump module 12, a control valve module 14, a spring cage assembly 16, a nozzle assembly 18, and a nozzle nut 20.
The pump module 12 comprises a pump body 22 with a central pumping cylinder 24 that receives a plunger 26. The cylinder 24 and the plunger 26 define a high-pressure cavity 28. In a well-known manner, the plunger 26 reciprocates within the cylinder 24 to increase fuel pressure in the high-pressure cavity 28. This action distributes pressurized fuel into a high-pressure passage 30 that exits at a face 31 in a large recess 33, formed in a lower end of the pump body 22.
The high-pressure passage 30 communicates with a high-pressure passage 32 in the control valve module 14 because an upper portion of the control valve module 14 is received within the large recess 33 so that an upper edge 34 of the control valve module 14 abuts the face 31 of the large recess. The face 31 requires a precision grinding process to insure the necessary flatness for a metal-to-metal seal. The high-pressure passage 32 extends generally linearly from the upper edge 34 to a lower edge 35 of the control valve module 14. A stator assembly 36 is centered within a recess 38 at the upper edge 34. A control valve 40 extends from the stator assembly 36 within a cylindrical chamber 42, and reciprocates in response to the respective forces of the stator assembly 36 and a spring 44. A high-pressure annulus 46 surrounding the control valve 40 is in communication with the high-pressure passage 32 by way of a cross passage 62.
At least one low-pressure passage or spill bore 48 extends from the cylindrical chamber 42 to a side edge of the control valve module 14 and communicates with a low-pressure reservoir 50 between the nozzle nut 20 and the control valve module 14. In a closed position, the control valve 40 blocks communication between the high-pressure passage 32 and the low-pressure passage 48. In an open position, the control valve 40 permits communication between the high-pressure passage 32 and the low-pressure passage 48.
A high-pressure passage 52 in the spring cage assembly 16 communicates at one end with the high-pressure passage 32 and at the other end with a high-pressure passage 54 in a stop plate 56. The high-pressure passage 54, in turn, connects with a passage 58 in the nozzle assembly 18. The nozzle nut 20 threadably attaches to the pump body 22 at a junction 60 and secures the nozzle assembly 18, stop plate 56, spring cage assembly 16, and control valve module 14 to the pump body 22. It has been found that the junction 60 is a point where fractures can occur because the axial flange forming the large recess 33 is a point of weakness.
In the present design, the high-pressure annulus 46 and the high-pressure passage 32 in the control valve module 14 are formed by drilling, followed by at least two electrochemical machining (ECM) procedures. The primary function of using an ECM process is to smooth sharp edges and burrs resulting from drilling or machining, thereby strengthening the control valve module. The cross passage 62 is drilled through the control valve module 14 to a T-connection with the high-pressure passage 32. A first ECM process at the T-connection has the effect of slightly enlarging the T-connection. A second ECM process is also used to form the high-pressure annulus 46. Thereafter, a plug or pin 64 (typically made of a shape memory alloy) is disposed in the cross passage 62 between the high-pressure annulus 46 and the edge of the control valve module 14. Also, the requirement for centering the stator assembly 36 in the recess 38 and the necessary for flatness in the metal-to-metal seal with the face 31 requires a precision grinding operation to maintain critical tolerances.
These processes are costly and time-consuming. There is a need to improve the ease and to lower the cost of manufacture, as well as to continually improve the performance of the control valve module during injection events.